How can I stop paint bubbling?

[MJDale]

Having prepared a previously painted plaster wall for re-painting I find that when I apply the new paint to the wall the old paint left underneath often bubbles as it gets wet. these bubbles will often - although not always - flatten out on drying. is there anything, short of removing ALL the old paint that I can do to the walls to stop this happening?

[incitatus]

I dont think so. Some of this bubbling may be due to moisture in the plaster, though, so running a dehumidifier in the room for a day or two may help. That said in similar situations Ive always had to remove the old paint.